As is the case with many human cancers, neuroectodermal tumors including melanoma and neuroblastoma are characterized by specific karyotypic abnormalities. The deletion of part of the chromosome region 1p12-pter resulting in monosomy for the deleted segment is one of the most commonly occurring abnormalities in both melanoma and neuroblastoma. The specific aims of this project are to analyze the role of the rearrangements and deletions of the short arm of human chromosome 1 in the series of events which ultimately result in the transformation of neural crest cells. By replacing the characteristically deleted fragment of the short arm of chromosome 1 with segments of chromosome 1 derived from normal human fibroblasts, it will be possible to determine whether there are recessive neuroectodermal tumor genes located within the monosomic segment of chromosome 1 in melanoma and neuroblastoma cells. Dominant selectable markers will be transfected into reduced mouse-human hybrid cells which contain either an intact chromosome 1 or segments of this chromosome. Microcell hybrids containing copies of the human chromosome 1 with an integrated dominant selectable marker will be isolated after a second round of hybridization to mouse cells. The different copies of human chromosome 1 will be transferred to recipient melanoma and neuroblastoma cells by microcell fusion, and the reconstituted neuroectodermal tumor cells will be tested for tumorigenicity in nude mice and for anchorage independent growth. Demonstration of the suppression of malignancy in melanoma and neuroblastoma cells after replacement of the deleted region on chromosome 1 with a homologous segment derived from normal human fibroblasts will confirm the presence of a recessive neuroectodermal tumor gene in the region 1p12-pter. Complementation studies of the suppression of malignancy in melanoma cells containing an intact neuroblastoma derived chromosome 1 will allow us to determine if the same locus is involved in the transformation of these different neuroectodermal tumors.